computers are rarely bad
it's been my experience with several vehicles other than the GC that computers are the most overly misdiagnosed fault in the industry. making things even more fishy is that they seem to be "rebuildable" by the manufacturer, thus requiring a "core" to return so you can't request the bad part be returned to the customer to see if it really was bad!
hard to tell if it's all a scam on the part of everyone involved or not. at the technician level it may look apparent that the computer is bad and replacing it seems to cure the problem but if the real issue is an intermittently bad sensor, the vehicle will come back again later when the issue rises again.
I remember speaking to someone in the tech department at Mid America Corvette (an aftermarket parts distributor independent of Chevrolet) and they were doing straight over rebuild exchanges of the ECM for $99.95, and the guy said 9 out of 10 that were sent in for rebuild were perfectly good.
the nature of the faults explained here by many GC owners indicate a similar situation, computers are getting replaced for numerous outside faults that pop up again later.